Process for preparing methyl- and ethyl-substituted primary anilines

ABSTRACT

A process is disclosed for the preparation of methyl- and ethyl-substituted anilines by contacting anilines of specified formula at about 250°-525° C. and about 10 kPa-10 MPa of pressure in the of presence of a nonbasic metal oxide catalyst which when it is a zeolite has pore dimensions of at least about 0.52 nm and has cages with dimensions greater than about 0.75 nm.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of application Ser. No. 559,184, filed Dec. 7, 1983, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to a process for the preparation of methyl- and ethyl-substituted anilines.

Methyl-substituted anilines are useful in a variety of applications such as in the preparation of dyes, herbicides, insecticides, plant growth agents and antiknock agents for gasoline engines. The anilines are generally prepared by nitration of the appropriate methyl benzene followed by reduction of the resulting nitro compound. This process depends upon the availability of the appropriate nitro compound which in some instances is unavailable or available only in limited quantities. For example, m-toluidine is important as an intermediate in dyes and agricultural chemicals. However, in the foregoing nitration-reduction process, only 4% of the toluidines produced are m-toluidine. As a result, separation of m-toluidine is a complex process and consequently the meta-isomer is the most expensive of the toluidines.

U.S. Pat. No. 3,868,420, issued to Evans et al. on Feb. 25, 1975, discloses a process for producing phenylamines alkylated in the ortho and/or para positions by alkyl groups of 1-4 carbon atoms and unsubstituted on the amino group which comprises reacting a suitable phenylamine with an alkanol of 1-4 carbon atoms in the vapor phase at a temperature of from 350° to 450° C. in the presence of an aluminum oxide catalyst or an aluminum oxide/molybdenum oxide mixed catalyst, said catalyst having a minimum surface area of 50 m² /g. U.S. Pat. No. 3,391,298, issued to Wollensak on Jan. 6, 1976, discloses a process for converting hydroxy-substituted aromatic compounds to the corresponding amine by reacting the aromatic hydroxy compound with ammonia in the presence of a catalytic amount of a cyclohexane and in contact with a hydrogen-transfer catalyst, most preferably palladium. U.S. Pat. No. 3,960,962, issued to Shubkin on June 1, 1976, discloses a similar process wherein the catalyst comprises metallic palladium bonded to a phosphinated polystyrene resin.

U.S. Pat. No. 4,188,341, issued to Fischer on Feb. 12, 1980, discloses a process for making 2,6-dimethylaniline or an N-substituted 2,6-dimethylaniline comprising reacting an enamine of a specified formula at a temperature of between -30° C. and 150° C. with acrolein in the presence of an inert aprotic solvent and heating the resulting reaction product to a temperature of between 100° and 400° C. in the presence of a hydrogen-transfer catalyst and an amine of the formula RNH₂ wherein R is --H or a specified lower alkyl.

Japanese Patent Application Publication Kokai No. 53-28128 discloses a process for para-methylation of anilines comprising reacting an aniline having para-hydrogens with methanol in the presence of an alkali metal synthetic zeolite catalyst, particularly NaY zeolite. Preparation of 2,4-dimethylaniline from o-toluidine and the preparation of p-toluidine from aniline are specifically disclosed.

T. Matsumoto, Chemistry Letters, p. 939 (1977), discloses the ortho-methylation of 2,3-dimethylaniline with methanol over various solid catalysts with 5 wt % Ag on Al₂ O₃ showing the highest selectivity to ortho-methylation, that is, the production of 2,3,6-trimethylaniline. M. Inoue and S. Enomoto, Sekiyu Gakkaishi, 15, 372 (1972) studied the methylation of aromatic compounds with methanol in vapor or liquid phase on various catalysts and specifically report the ortho-methylation of aniline with methanol using 10% MgO/Al₂ O₃ catalyst to produce o-toluidine.

Japanese Patent Publication 28129/1978 discloses demethylation of polymethylanilines, which contain at least more than two methyl groups, in the presence of a catalyst composition of the formula A_(a) B_(b) C_(c) O_(d) wherein A is titanium; B represents more than one kind of element selected from zinc, zirconium and magnesium; C represents more than one kind of element, selected from vanadium, chromium, manganese, tin, iron, cobalt, nickel, copper, molybdenum, tungsten, barium, calcium; O is oxygen; a is 1, b is 0.05 to about 20, and c is 0 to 1.0. Reaction temperatures of 440°-600° C. are disclosed. Ti-Zr catalyst systems are stated to give mainly p-demethylated products, such as 2,6-xylidine from mesidine. Ti-Zn or Mg catalyst systems give o- and/or p-demethylated products, such as m-toluidine from 2,3-, 3,4-, and 2,5-dimethylaniline, 2,4,5-trimethylaniline; and 2,3,4,6-tetramethylaniline.

Japanese Patent Publication No. 1974-[Showa-49], 29,178 discloses a process for the synthesis of toluidines rich in m-toluidine by dealkylation of xylidines having a methyl group in a meta position at 400°-700° C. in the presence of a dealkylation catalyst such as silica-alumina, alumina, silica, silica-magnesia and magnesia. Matsumoto et al., Chemistry Letters, pp 435-438 (1978) discloses a process for preparing m-toluidine by hydrocracking 2,3-xylidine over metal oxide-supported nickel catalysts. The authors disclose that the selectivity of m-toluidine is influenced by side reactions, such as isomerization, and that the extent of isomerization can be related to the acidic character of the metal oxide carriers.

SUMMARY OF THE INVENTION

The present invention provides a process for preparing one or more substituted anilines of the formula ##STR1## wherein R is --CH₃ or --C₂ H₅ and n is 1 or 2 comprising contacting an aniline of the formula ##STR2## with an aniline of the formula ##STR3## wherein R₁ and R₂ are both methyl or ethyl, n₁ and n₂ are different and are individually an integer from 0 to 3, and n₁ +n₂ is an integer from 1 to 5, said contacting being performed in the presence of a nonbasic metal oxide catalyst at a temperature of from about 250° to about 525° C. and at a pressure of from about 10 kPa to about 10 MPa, the formula I product being different from the formulae II and III starting materials and the total number of R groups attached to the resulting products being equal to the total number of R groups attached to the starting aniline; with the proviso that when the nonbasic metal oxide catalyst is a zeolite it has pore dimensions of at least about 0.52 nm and has cages with dimensions greater than about 0.75 nm.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE shows the kinetic paths followed by m- and p-toluidines in the presence of aniline to reach equilibrium when equilibration takes place over HY zeolite.

DETAILED DESCRIPTION OF THE INVENTION

Transmethylation is represented by the reaction ##STR4## where n₁, n₂, n₃, and n₄ represent the number of methyl groups on each aniline and n₁ +n₂ is an integer from 1 to 5 with the proviso that n₁ and n₂ are different and are individually an integer from 0 to 3 and n₁ +n₂ equals n₃ +n₄. The product can contain one or more isomers corresponding to a given number of methyl groups.

Transethylation proceeds in a similar manner.

The process of the invention includes

(a) the production of toluidine and dimethylaniline from aniline and 2,4,6-trimethylaniline;

(b) the production of dimethylanilines from toluidine and 2,4,6-trimethylaniline;

(c) the production of toluidines from dimethylanilines and aniline; and

(d) the production of isomers of a dimethylaniline and of a toluidine.

Catalysts suitable for the present process include molecular sieves, i.e., type X and Y zeolites, silica, alumina, silica-alumina compositions, titania, zironia, iron oxide, zinc oxide and Group V and VI metal oxides. Molecular sieves are commercially available as are many of the other suitable catalysts. Metal oxide catalyst compositions for use as catalysts in the present invention can be prepared by impregnating a substrate with a solution(s) containing the desired oxide(s), coprecipitating the desired materials on the substrate or by evaporation or spattering techniques well known in the art. When the catalyst is other than a molecular sieve it is preferably amorphous.

When the nonbasic metal oxide is a zeolite (molecular sieve) it has pore dimensions of at least about 0.52 nm and has cages with dimensions greater than about 0.75 nm. One skilled in the art will recognize that as the number of methyl or ethyl groups on the reactants increases, the minimum pore and cage dimensions must increase correspondingly. The zeolites X and Y are suitable in general for the transalkylation process of the invention. As used herein pore dimensions mean the aperture dimensions determined from crystal structure analyses, i.e., the crystallographic free diameters of the channels as discussed by W. M. Meier and D. H. Olson, "Atlas of Zeolite Structure Types", published by the Structure Commission of the International Zeolite Associations, 1978. The free diameter values are based on the atomic conditions of the type species in the hydrated state and an oxygen radius of 1.35 Å (0.135 nm).

In the process of the invention, the total number of methyl or ethyl groups on the primary anilines is substantially conserved. Minor portions of one or more reactants may undergo reactions in which some of the methyl or ethyl groups are lost by the anilines. However, except at the highest temperatures, the major portions of the reactants undergo the foregoing transalkylation reaction in which the number of methyl or ethyl groups on the reactant anilines equals the number on the product anilines.

The efficiency of a particular transalkylation is determined by the two substituted aniline reactants and the catalyst. The ease of the reaction increases as the sum of n₁ +n₂ increases from one to five. Nonbasic oxides can catalyze the transalkylation of aniline and 2,4,6-trimethylaniline (TMA). Acidic oxides, but not neutral ones, catalyze transalkylations where n₁ +n₂ =2 but strong acids, such as the hydrogen-exchanged Y zeolite (HY) and other silica-alumina compositions, are required when n₁ +n₂ =1. A discussion of acidic strengths is contained in K. Tanabe, "Solid Acids and Bases", Academic Press, New York (1970).

A specific transmethylation is the reaction of aniline and 2,4,6-trimethylaniline over a nonbasic metal oxide catalyst to produce 2,4- and 2,6-dimethylaniline and o- and p-toluidine. The different metal oxide catalysts redistribute the methyl groups between 2,4,6-trimethylaniline and aniline differently and can be grouped according the the selectivity they show toward producing either 2,6-dimethylaniline and p-toluidine or 2,4-dimethylaniline and o-toluidine. In general, all four products are present to some degree and, in addition, there may also be small amounts of m-toluidine and other dimethylanilines.

Silica-aluminas show high selectivity to 2,6-dimethylaniline and p-toluidine, that is, to the transfer of the methyl from the para-position of 2,4,6-trimethylaniline to the para-position of aniline. The larger pore zeolites, such as zeolites X and Y, are examples of such catalysts, and the zeolite HY and the rare earth-exchanged X zeolite (REX) are especially preferred. Silica-alumina compositions include those ranging from pure silica to pure alumina.

In contrast, supported titania, zirconia, iron oxide, zinc oxide, and Group V and VI metal oxides show good selectivity to 2,4-dimethylaniline and o-toluidine, that is, to the transfer of the methyl from the ortho-position of 2,4,6-trimethylaniline to the ortho-position of aniline.

Each of these two groups of catalysts is more selective to the particular dimethylaniline and toluidine at lower operating temperatures and shorter contact times. In general, as the reaction conditions become increasingly severe, by raising the temperature and/or increasing the contact time, overall conversion is increased but selectivity to the particular dimethylaniline and toluidine is reduced. The process of the invention is conducted at a temperature of from about 250° to about 525° C., preferably from about 300° to 400° C., and at a pressure of from about 10 kPa (0.1 atmospheres) to about 10 MPa (100 atmospheres) for a period of time from about 0.1 sec to about 10 hours. The process of the invention can be carried out in either a liquid or gas phase. Times of about 1 sec and 0.5 hr will often be suitable for vapor phase and liquid phase reactions, respectively. Preferably, a pressure of about 1 atmosphere is used for vapor-phase reactions and autogenous pressure is used for liquid-phase reactions.

Some of the same metal oxides useful as a catalyst in the reaction of aniline and 2,4,6-trimethylaniline are also useful as a catalyst in the other transmethylation processes of this invention and in particular for the transmethylation represented by the reaction: ##STR5## where the product aniline with n₁ is a different isomer than the reactant aniline with n₁ and the anilines with n₂ represent the same isomer. In essence, the aniline with (CH₃)_(n).sbsb.2 is a co-catalyst for the isomerization of the aniline with (CH₃)_(n).sbsb.1 creating a transmethylation process which in effect results in the equilibration of one of the reactants. For these equilibration processes useful catalysts are determined by the same rules concerning the sum of n₁ +n₂ as set forth earlier herein.

Equilibration of 2,4- and 2,6-dimethylaniline occurs when one or both of these isomers is reacted with either o-toluidine or 2,4,6-trimethylaniline. The product can also contain some aniline, p- and m-toluidine and, when o-toluidine is a reactant, 2,4,6-trimethylaniline. Equilibration of 2,3-, 2,5-, and 3,4-dimethylanilines occurs when one or more of these isomers is reacted with m-toluidine. The product can also contain small amounts of 2,4- and 2,6-dimethylanilines.

Toluidine equilibration occurs when one or more toluidines are reacted with aniline. The ortho and para isomers are rapidly interconverted and the resulting two component equilibrium mix and the meta isomer then slowly approach the three component equilibrium (17% p-, 31% o-, and 52% m-toluidine). This equilibration in the presence of HY zeolite catalyst is the basis for the theoretical lines shown in the FIGURE. However, there are competing reactions. While a 10% solution of o-toluidine in aniline approximates the theoretical line shown in the FIGURE, a 1:1 mix of aniline and o-toluidine does not follow the curve, but bends toward the three component equilibrium much earlier, and pure o-toluidine proceeds almost straight to the three component equilibrium. The disproportionation of two o-toluidines to a dimethylaniline and aniline appears to be competitive with the reaction of o-toluidine and aniline to give p-toluidine and aniline, but can be controlled by working with an excess of aniline. For equilibration the co-catalyst should be present in an amount sufficient to ensure that the equilibration reaction dominates over reactions involving solely one of the reactants.

The invention is further illustrated by the following examples in which all temperatures are in degrees Celsius and all percentages are by weight unless otherwise stated.

EXAMPLE 1

A solution of equimolar amounts of aniline and 2,4,6-trimethylaniline was passed over 3 g of HY zeolite catalyst at atmospheric pressure and a temperature of 300°-400°, at a flow rate of 2 ml/hr with a nitrogen gas flow rate of 40 ml/min, in a 13 cm (5 inch) long--1 cm (3/8 inch) diameter, heat resistant glass reactor heated with a split tube furnace. The HY zeolite used in this and later examples had a unit cell dimension of 24.45 Å, a SiO₂ /Al₂ O₃ ratio of 3.31, and a Na₂ O content of 0.15%. This process was continued for 30 minutes at a fixed reaction temperature, e.g., 300°, and the resulting liquid effluent collected. The foregoing steps were then repeated at temperatures of 350° and 400°. Each resulting product was analyzed by gas chromatography using a 6.1 m (20 ft) by 0.32 cm (1/8 inch) stainless steel column packed with polyethylene oxide of a molecular weight of about 200,000 and 1% KOH on 80/100 mesh diatomaceous earth. Elution was carried out isothermally at 200° with a nitrogen gas flow or 40 cc/minute. Retention times increase in the order aniline, ortho-, para- and meta-toluidine, 2,6- and 2,4-dimethylaniline (DMA) and 2,4,6-trimethylaniline (TMA). The results are summarized in Table I. Selectivity to 2,6-dimethylaniline (2,6-DMA) is defined as the percentage of DMA product that is 2,6-DMA, i.e., ##EQU1## where the quantities of 2,6-DMA and 2,4-DMA are in moles. The selectivity to p-toluidine is similarly defined as ##EQU2## Likewise, 2,4,6-TMA conversion is defined as ##EQU3## The amount of m-toluidine and other DMA isomers in each product was negligible. As the reaction temperature increased, the conversion of 2,4,6-TMA increased; however, selectivity to 2,6-DMA and to p-toluidine decreased.

EXAMPLES 2-11

Aniline and 2,4,6-TMA were reacted over other silica-alumina catalysts that show high selectivity to 2,6-DMA and p-toluidine in a manner similar to that described in Example 1. The process conditions and results are summarized in Table I. In each example, 3 g of catalyst were used, reactor effluent obtained during the first 25 minutes of operation was discarded, and product obtained during the next 5 minutes of operation was collected and analyzed using gas chromatography. A 3.0 m (10 foot)×0.32 cm (1/8 inch) stainless steel column packed with 2% UCON 50 HB 5100 and 1.0% KOH on 80/100 mesh diatomaceous earth was used to characterize the product. A helium gas flow of 25 ml/min was used and elution was carried out at 150°. Elution of all peaks of interest took place within 14 minutes.

EXAMPLES 12-22

Aniline and 2,4,6-TMA were reacted over the titania, zirconia and other Group V and VI metal oxide catalysts which show good selectivity to 2,4-DMA and o-toluidine in a manner similar to that described for Examples 2-11 and the process conditions and results are summarized in Table I. Note that a low selectivity to 2,6-DMA and p-toluidine represents a correspondingly high selectivity to 2,4-DMA and o-toluidine, respectively.

EXAMPLES 23-26

In order to demonstrate liquid phase reaction of aniline and 2,4,6-TMA, 2 ml of an aniline-2,4,6-TMA solution and 0.5 g catalyst were placed in a shaker tube which was then evacuated at room temperature and sealed. The tube was heated to a desired reaction temperature, shaken for a given time, and was then cooled to room temperature. The contents of the tube were analyzed by gas chromatography using a procedure similar to that described in Examples 2-10. Process conditions are listed and results summarized in Table II.

EXAMPLES 27-29

The use of nonbasic metal oxide catalysts to equilibrate anilines by a transmethylation process was demonstrated in a manner similar to that used to demonstrate the transmethylation process described in Example 1. A solution of o-toluidine and 2,4- and/or 2,6-DMA was passed over 3 g of HY zeolite catalyst at atmospheric pressure and a given reaction temperature at a flow rate of 3 ml/hr with a nitrogen gas flow rate of 10 ml/min in a vapor phase reactor similar to that used in Example 1. Liquid effluent was collected and analyzed by gas chromatography using a procedure similar to that described in Examples 2-10. The process conditions used for each example and the results are summarized in Table III. The product can contain aniline, p- and m-toluidine, and 2,4,6-TMA in addition to the 2,4- and 2,6-DMA and o-toluidine.

                                      TABLE I                                      __________________________________________________________________________                  Feed                                                                           Ratio Feed                                                                               N.sub.2                                                                            Re-                                                              Aniline:                                                                             Flow                                                                               Gas action                                                                              Conversion                                                                           Selectivity                                                                          Selectivity                        Example      2,4,6-TMA                                                                            Rate                                                                               Flow                                                                               Temp of    to    to                                 No.  Catalyst                                                                               (moles)                                                                              ml/hr                                                                              ml/min                                                                             (degrees)                                                                           2,4,6-TMA                                                                            2,6-DMA                                                                              p-toluidine                        __________________________________________________________________________     1    HY Zeolite                                                                             1     2   40  300  62    92    67                                                            350  77    58    46                                                            400  85    55    28                                 2    91% Al.sub.2 O.sub.3 /6%                                                               1     3   10  375  15    79    88                                      SiO.sub.2             450  64    52    47                                 3    10%     2     3   10  375   8    82    100                                     Al.sub.2 O.sub.3 /SiO.sub.2                                                                          450  38    59    61                                 4    12%     2     3   10  300   6    92    100                                     Al.sub.2 O.sub.3 /86% 375  40    83    88                                      SiO.sub.2             450  81    57    53                                 5    Attapulgus                                                                             1     3   10  300   7    78    92                                      Clay                  375  17    66    81                                                            450  40    46    64                                 6    Bentonite Clay                                                                         2     3   10  300  30    86    91                                                            375  29    71    82                                                            450  39    48    60                                 7    Kaolinite Clay                                                                         2     3   10  450  15    50    65                                 8    SiO.sub.2                                                                              1     3   10  450  17    47    63                                 9    99% Al.sub.2 O.sub.3                                                                   1     3   10  375   3    50    75                                                            450  29    38    51                                 10   HY Zeolite                                                                             3.5   3   10  260  51    92    76                                                    3   10  290  80    85    68                                                    1.5 25  260  68    87    78                                                    1.5 50  260  53    88    85                                 11   REX Zeolite                                                                            1     2   40  300  59    83    Not                                                                            measured                                                      350  73    60                                       12   TiO.sub.2                                                                              1     3   10  475  15     8    36                                 13   ZrO.sub.2                                                                              1     3   10  375   2    43    50                                                            450  44    41    45                                 14   10% ZnO/TiO.sub.2                                                                      1     3   10  450  17     8    30                                 15   Sb/9Ti/O                                                                               1     3   10  375  19    21    25                                                            450  43    18    39                                 16   10%     2     3   10  375  14    25    39                                      MoO.sub.3 /Al.sub.2 O.sub.3                                                                          400  46    18    33                                 17   19%     1     2   40  500  51    17    31                                      Cr.sub.2 O.sub.3 /Al.sub.2 O.sub.3                                                     2     3   10  450  26    10    30                                 18   24%     2     3   10  450  10    20    50                                      ZnO/Al.sub.2 O.sub.3                                                      19   10%     2     3   10  375   4     0    50                                      ZnO/10%               450  48    18    40                                      Cr.sub.2 O.sub.3 /Al.sub.2 O.sub.3                                        20   10%     2     3   10  375  22    68    54                                      WO.sub.3 /Al.sub.2 O.sub.3                                                                           450  56    38    52                                 21   10%     2     3   10  375   8    14    31                                      V.sub.2 O.sub.5 /Al.sub.2 O.sub.3                                                                    450  21     0    24                                 22   20%     2     3   10  375   5     0    100                                     Fe.sub.2 O.sub.3 /Al.sub.2 O.sub.3                                                                   450  17    26    48                                 __________________________________________________________________________

                                      TABLE II                                     __________________________________________________________________________                 Feed Ratio                                                                     Aniline                                                                              Reaction                                                                            Reaction                                                                            Conversion                                                                           Selectivity                                                                          Selectivity                            Example     2,4,6-TMA                                                                            Temp Time of    to    to                                     No.  Catalyst                                                                              (moles)                                                                              (degrees)                                                                           (hr) 2,4,6-TMA                                                                            2,6-DMA                                                                              p-Toluidine                            __________________________________________________________________________     23   HY Zeolite                                                                            2     350  2    71    94    76                                                       375  2    75    86    62                                                       350  4    69    91    75                                                       350  8    76    89    65                                                       375  1    70    88    71                                     24   91% Al.sub.2 O.sub.3 /                                                                1     300  2    21    93    92                                          6% SiO.sub.2                                                                   (Amorphous)                                                               25   87% SiO.sub.2 /                                                                       1     300  2    12    93    100                                         13% Al.sub.2 O.sub.3                                                           Amorphous                                                                 26   Sb/9Ti/O                                                                              2     350  2     6    42    33                                     __________________________________________________________________________

                                      TABLE III                                    __________________________________________________________________________                               Product                                               Example                                                                             Feed Composition (mole %)                                                                      TempReaction                                                                        ##STR6##                                            No.  o-Toluidine                                                                          2,4-DMA                                                                             2,6-DMA                                                                             (degrees)                                                                           (mole percent)                                       __________________________________________________________________________     27   52.7  43.4 --   296   1                                                                        308   2                                                                        338   5                                                                        340  16                                                                        350   8                                                                        393  18                                                   28   42.6  --   55.9 290  85                                                                        306  50                                                                        325  47                                                                        334  49                                                                        348  52                                                                        365  50                                                   29   47.9  22.3 29.8 282  55                                                                        321  49                                                                        349  45                                                                        368  43                                                                        387  43                                                                        406  47                                                   __________________________________________________________________________

EXAMPLES 30-31

2,4- and 2,6-DMA were equilibrated by reacting them with 2,4,6-TMA over HY zeolite catalyst using a procedure similar to that used for Examples 27-29. The results are summarized in Table IV.

EXAMPLES 32-34

Equilibration of 2,3-, 2,5-, and 3,4-DMA by reacting each with m-toluidine over the HY zeolite catalyst was carried out using a procedure similar to that described for Examples 27-29. The results are given in Table V. The product can also contain some aniline, o- and p-toluidine, and 2,4- and 2,6-DMA.

EXAMPLES 35-39

Equilibration of toluidines in the presence of HY zeolite was carried out in a manner similar to that used for Examples 27-29: 3 g of HY zeolite were used, the feed solution flow rate was 3 ml/hr in each case and the nitrogen flow rate was 10 ml/min. Results are summarized in Table VI. As can be seen from Example 35, the ortho and para isomers are nearly completely equilibrated before any appreciable amount of meta begins to form. Examples 37, 38 and 39 show the role played by aniline when HY catalyst is used as well as the importance of the disproportionation of toluidines to DMA's and aniline (Example 39). On the basis of beginning with p-toluidine/aniline and m-toluidine/aniline feeds, the three component equilibrium is approached as shown in FIG. 1. While a 10% solution of ortho-toluidine in aniline approaches the curve shown, a 1:1 mix of aniline and o-toluidine does not follow the curve, but bends toward the three component equilibrium much earlier. Pure o-toluidine proceeds almost straight to the three component equilibrium.

                                      TABLE IV                                     __________________________________________________________________________                               Product                                               Example                                                                             Feed Composition (mole %)                                                                      TempReaction                                                                        ##STR7##                                            No.  2,4,6-TMA                                                                            2,4-DMA                                                                             2,6-DMA                                                                             (degrees)                                                                           (mole percent)                                       __________________________________________________________________________     30   48    --   53   252  96                                                                        273  95                                                                        310  79                                                                        340  38                                                                        363  37                                                                        405  40                                                                        435  46                                                                        471  51                                                                        502  68                                                   31   44    56   --   290   7                                                                        318  19                                                                        355  28                                                                        387  33                                                                        423  27                                                                        467  30                                                                        501  25                                                   __________________________________________________________________________

                                      TABLE V                                      __________________________________________________________________________     Feed Composition        Product Composition (mole %)                                m-            Reaction                                                    Example                                                                             toluidine                                                                           DMA      Temp m-                                                     No.  (mole %)                                                                            (isomer/mole %)                                                                         °                                                                            toluidine                                                                           2,3-DMA                                                                             3,4-DMA                                                                             2,5-DMA                                 __________________________________________________________________________     32   53   2,3-DMA/46                                                                              293  43   46   --   --                                                         322  54   40   2.0  1.3                                                        346  57   35   2.8  2.4                                                        382  58   31   3.8  4.1                                                        420  56   21   4.8  7.4                                     33   52   3,4-DMA/44                                                                              282  61   --   39   --                                                         341  64   0.7  31   3.3                                                        371  64   1.3  27   6.4                                                        405  65   2.2  24   8.0                                                        438  62   5.3  16   11                                                         460  55   6.9  10   11                                                         483  50   7.8  8.8  9.4                                                        508  48   6.0  12   7.2                                     34   53   2,5-DMA/45                                                                              302  54   0.8  --   44                                                         320  57   1.1  4.7  36                                                         340  57   1.2  4.8  35                                                         363  57   4.6  4.9  31                                                         391  58   3.5  5.7  27                                                         403  46   5.2  6.3  23                                                         423  50   6.5  5.5  16                                                         453  45   6.9  4.8  14                                                         473  44   5.9  3.9  13                                      __________________________________________________________________________

                                      TABLE VI                                     __________________________________________________________________________     Feed        Reaction                                                                            Product Composition (mole %)                                  Example                                                                             Composition                                                                           Temp     o-   p-   m-   2,6-                                                                               2,4-                                                                               2,4,6-                             No.  (mole ratio)                                                                          °                                                                            Aniline                                                                            toluidine                                                                           toluidine                                                                           toluidine                                                                           DMA DMA TMA                                __________________________________________________________________________     35   0.3 o-tolu-                                                                           375  63  18   13   1.1  1.1 3.6 6.4                                     idine:0.7                                                                             397  54  18   16   1.0  1.6 --  --                                      p-toluidine:1                                                                         440  63  18   11   3.5  1.0 3.1 0.6                                     aniline                                                                               447  68  17   11   4.3  2.6 6.6 --                                             462  64  16   11   5.5  2.3 0.8 0.1                                            480  67  15   9.6  8.3  --  --  --                                             500  70  12   6.0  9.2  0.3 0.9 0.7                                36   1-m-tolu-                                                                             290  52  --   --   46   --  1.4 0.2                                     idine:1                                                                               320  53  --   0.1  46   --  0.4 0.1                                     aniline                                                                               354  53  0.3  0.3  46   --  0.3 0.2                                            407  52  0.9  0.8  46   --  0.5 0.3                                            454  54  3.0  2.1  39   --  0.9 0.5                                            500  59  5.3  3.6  30   0.3 0.9 0.6                                37   1-o-tolu-                                                                             375  56  30   6.7  1.0  1.1 3.8 0.4                                     idine:1                                                                               392  56  29   6.6  1.3  1.1 3.4 0.3                                     aniline                                                                               409  56  30   6.1  1.8  1.1 3.5 --                                             437  59  27   5.5  3.7  0.7 2.4 0.3                                            453  60  26   5.2  5.0  0.6 1.7 0.4                                            473  63  24   4.8  6.5  --  0.8 --                                 38   .11-o- 317  88  11   --   --   --  --  --                                      toluidine:                                                                            357  88  9.3  1.5  0.2  0.1 0.1 0.2                                     .89 aniline                                                                           402  88  7.1  2.9  0.5  0.2 0.2 0.3                                            415  90  9.1  0.7  0.2  --  --  --                                             423  90  6.9  2.4  0.5  --  --  0.5                                            444  90  6.2  2.2  0.8  --  --  0.4                                            451  90  6.9  1.4  0.8  --  --  0.3                                            468  91  5.3  1.8  1.3  --  --  0.3                                            489  92  3.9  1.3  1.8  --  --  --                                 39   o-toluidine                                                                           370  21  59   --   --   3.1 16  1.0                                            388  20  57   4.6  1.0  3.0 13  0.6                                            403  24  56   --   --   3.4 15  1.3                                            422  18  60   2.6  2.2  2.3 10  0.9                                            441  13  76   1.6  3.1  1.9 6.6 0.7                                            469  20  52   3.7  5.8  2.4 6.8 1.5                                            492  24  53   4.8  8.2  2.5 6.0 2.0                                __________________________________________________________________________

EXAMPLE 40-48

Equilibration of toluidines in the presence of other catalysts was conducted by using a procedure similar to that used for Examples 27-29: 3 g of catalyst were used, the feed solution flow rate was 2.2 ml/hr and the nitrogen flow rate was 10 ml/min. Results are shown in Table VII.

EXAMPLES 49-50

Equilibration of ethylanilines in the presence of HY zeolite was conducted by using a procedure similar to that used in Examples 27-29. A solution of aniline and either p-ethylaniline or o-ethylaniline was passed over 3 g of HY zeolite catalyst at atmospheric pressure and a given reaction temperature at a flow rate of 2.2 ml/hr with a nitrogen gas flow rate of 10 ml/min. The relative amounts of aniline and ethylanilines in the product are shown in Table VIII. There was also a small fraction of high-boiling unidentified material in the product.

                                      TABLE VII                                    __________________________________________________________________________             Feed   Reaction                                                                            Product Composition (mole %)                               Ex.     Composition                                                                           Temp     o-   p-   m-   2,6-                                                                               2,4-                                                                               2,4,6-                          No.                                                                               Catalyst                                                                            (mole ratio)                                                                          (degrees)                                                                           Aniline                                                                            toluidine                                                                           toluidine                                                                           toluidine                                                                           DMA DMA TMA                             __________________________________________________________________________     40 (1)  1 p-tolui-                                                                            300  75  12   8.0  2.4  0.4 0.3 0.7                                     dine:1 aniline                                                         41 (2)  1 p-tolui-                                                                            375  56  --   43   --   0.5 --  --                                      dine:1 aniline                                                                        500  68  6.0  22   1.0  2.0 --  --                              42 (3)  1 p-tolui-                                                                            375  54  --   46   --   --  --                                          dine:1 aniline                                                                        500  66  4.3  26   0.3  2.4 --                                  43 (4)  1 p-tolui-                                                                            400  54  --   46   --   --  --  --                                      dine:1 aniline                                                                        500  65  2.9  29   --   2.2 --  --                              44 (5)  1 p-tolui-                                                                            375  64  4.3  29   3.5  --  --                                          dine:1 aniline                                                                        500  51  --   49   --   0.5 --                                  45 (6)  1 p-tolui-                                                                            375  57  0.6  41   --   1.1 --  --                                      dine:1 aniline                                                                        500  65  1.5  32   0.6  0.9 --  --                              46 (7)  1 o-tolui-                                                                            500  73  24   1.7  0.7  0.4 0.5 --                                      dine: 2 aniline                                                                       500  79  18   1.6  0.6  0.2 0.4 --                              47 (8)  1 o-tolui-                                                                            500  77  19   0.9  1.7  0.2 0.2 --                                      dine:2 aniline                                                         48 (9)  1 o-tolui-                                                                            500  82  15   1.0  0.9  --  --  --                                      dine:2 aniline                                                         __________________________________________________________________________      (1) HY                                                                         (2) 91% Al.sub.2 O.sub.3 /6% SiO.sub.2 (amorphous)                             (3) 99% Al.sub.2 O.sub.3                                                       (4) 99% Al.sub. 2 O.sub.3                                                      (5) 87% SiO.sub.2 /13% Al.sub.2 O.sub.3                                        (6) 10% MoO.sub.3 /Al.sub.2 O.sub.3                                            (7) 33% Cr.sub.2 O.sub.3 /Al.sub.2 O.sub.3                                     (8) 10% MoO.sub.3 /Al.sub.2 O.sub.3                                            (9) 10% V.sub.2 O.sub.5 /SiO.sub.2 - containing Al.sub.2 O.sub.3         

                  TABLE VIII                                                       ______________________________________                                                         Product Composition (mole %)                                   Exam- Feed       Reaction      o-    p-    m-                                  ple   Composition                                                                               Temp     Anil-                                                                               ethyl-                                                                               ethyl-                                                                               ethyl-                              No.   (mole ratio)                                                                              (degrees)                                                                               ine  aniline                                                                              aniline                                                                              aniline                             ______________________________________                                         49    1 p-ethyl- 300      55   4.0   41    --                                        aniline:1  330      58   10    32    --                                        aniline    360      60   15    25    --                                                   390      66   13    16    4.4                                                  420      76   6.6   6.9   10                                  50    1 o-ethyl- 275      46   53    0.6   --                                        aniline:1  300      49   49    1.9   --                                        aniline    330      53   39    7.5   --                                                   360      58   28    12    2.5                                                  390      60   24    14    2.4                                                  420      58   16    11    5.3                                 ______________________________________                                     

The invention being claimed is:
 1. A process for preparing 2,6-dimethylaniline and p-toluidine or 2,4-dimethylaniline and o-toluidine, by transalkylation of 2,4,6-trimethylaniline and aniline, comprising contacting 2,4,6-trimethylaniline and aniline in the presence of a nonbasic metal oxide catalyst at a temperature from about 250° to 525° C. and a pressure from about 10 kPa to 10 MPA, characterized in that, when the catalyst is a silica-alumina, the process is selective for 2,6-dimethylaniline and p-toluidine and, when the catalyst is supported titania, zirconia, iron oxide, zinc oxide and Group V and Group VI metal oxides, the process is selective for 2,4-dimethylaniline and o-toluidine, with the proviso that where the catalyst is a zeolite it has pore dimensions of at least about 0.52 nm and cages with dimensions greater than 0.75 nm.
 2. A process according to claim 1, conducted at a temperature from about 300° C. to about 500° C.
 3. A process according to claim 2 which exhibits selectivity for 2,6-dimethylaniline and p-toluidine, wherein the catalyst is a silica-alumina catalyst.
 4. A process according to claim 3, wherein the catalyst is a type X or type Y zeolite.
 5. A process according to claim 4, wherein the catalyst is a hydrogen-exchanged type Y zeolite or a rare earth-exchanged type X zeolite.
 6. A process according to claim 5, wherein the catalyst is a hydrogen-exchanged type Y zeolite.
 7. A process according to claim 2 which exhibits selectivity for 2,4-dimethylaniline and o-toluidine, wherein the catalyst is selected from the group consisting of supported titania, zirconia, iron oxide, zinc oxide, and Group V and VI metal oxides. 